1. Field of the Invention
The invention relates to a method for producing a vacuum between two sheets of glass and insulating glazing thus produced.
The method according to the invention, although it is not limited to the production of insulating glazing, will be described more particularly by reference to this applications
2. Discussion of the Background
It is usual, in order to obtain thermal and/or acoustic insulation, to produce insulating glazing including two sheets of glass separated from one another by a relatively thick air gap. Such glazing provides thermal insulation which is judged to be insufficient for certain occasions. To remedy that, it is known to produce glazing including three sheets of glass and one of the air gaps can be replaced by a gas, for example krypton. This glazing has markedly enhanced thermal insulation properties, but is so thick that it is not always easy to use it.
Moreover, current demand from the users is turning towards thermal insulation of glazing equivalent to that of solid walls. Insulating glazing had already been proposed, particularly in Patent No. WO-91/02878, consisting of two sheets of glass separated from one another by a space in which a vacuum has been produced.
This glazing, due to the vacuum, achieves very good insulation but it is very difficult to produce. On the one hand, the slight thickness between the two sheets of glass, which is of a few tenths of a millimeter, has to be constant over the whole region where the sheets of glass are face-to-face.
Moreover, a perfectly leaktight seal has to be formed between the two sheets of glass.
Patent No. WO-91/02878 describes a technique consisting in placing studs a few tenths of a millimeter thick on one of the sheets of glass, which are distributed over the whole surface, and, at the same time, a joint which will allow the two sheets of glass to be sealed. These studs and this seal are produced in the same material, which is a glass-making composition. It is apparent that this glazing is difficult to produce due to these simultaneous operations which require intricate handling.
Moreover, the sealing joint has a number of bubbles which can impair the leaktightness and the aesthetics.
This patent also describes a method for forming the vacuum between the two sheets of glass. It particularly proposes inserting a tube between the two sheets of glass before sealing, to which a connection is made in order to pump out the air. Another embodiment consists in piercing a hole through one of the sheets of glass and in pumping out the air through this orifice.
In the first case, it is necessary to seal the tube in a leaktight fashion at the same time as the sheets of glass, which makes the operations difficult. Moreover, it is necessary, after having formed the vacuum, to seal the end of the tube, then to protect this end in order to avoid breaking.
In the second case, the vacuum is formed by means of a tube previously sealed around the hole. Then, after having formed the vacuum, this tube is melted so as to seal its end. The disadvantage of these embodiments is that the insulating glazing provided has a fragile point either on the periphery or on one surface. In the second case, part of the tube remains outside the glazing, which increases the risks of damage.